The present invention regards a process for manufacturing a group comprising at least two elements, one whereof includes an encapsulated micro-integrated structure, and a thereby obtained group. In particular, the invention may be advantageously applied for assembling a microactuator, an integrated device including microactuator control circuitry and a head in a hard-disk read/write unit with double micrometric actuation.
As is known, hard disks are the most widely used data-storage medium; consequently, they are produced in very large volumes, and the maximum data-storage density increases from one year to the next. Hard disks are read and written by actuator devices, the general structure of which is shown in FIGS. 1 and 2 and is described hereinafter.
In particular, FIG. 1 shows a known actuator device 1 of the rotary type comprising a motor 2 (also called xe2x80x9cvoice coil motorxe2x80x9d) fixed to a support body, generally called xe2x80x9cE-blockxe2x80x9d because of its E-like shape in side view (see FIG. 2). The support body 3 has a plurality of arms 4, each of which carries a suspension 5 including a cantilevered lamina. At its end not fixed to the support body 3, each suspension 5 carries a R/W transducer 6 for reading/writing, arranged (in an operative condition) facing a surface of a hard disk 7 so as to perform roll and pitch movements and to follow the surface of the hard disk 7. To this end, the R/W transducer 6 (also referred to as slider) is fixed to a joint, called gimbal or flexure 8, generally formed from the suspension 5 and comprising, for example, a rectangular plate 8a cut on three and a half sides starting from the lamina of the suspension 5, and having a portion 8b connected to the suspension 5 and allowing flexure of the plate 8a under the weight of the slider 6 (see FIG. 2A)
In order to increase the data storage density, it has already been proposed to use a double actuation stage, with a first, rougher actuation stage including the motor 2 moving the assembly formed by the support body 3, the suspension 5 and the R/W slider 6 through the hard disk 7 during a coarse search for the track, and a second actuation stage performing a finer control of position of the slider 6 during tracking. According to a known solution, the second actuation stage comprises a microactuator 10 arranged between the gimbal 8 and the slider 6, as may be seen in FIG. 3, which shows, in exploded view, the end of the suspension 5, the gimbal 8, the slider 6, and the microactuator 10, in this case, of the rotary type. The microactuator 10 is controlled by a signal supplied by control electronics on the basis of a tracking error.
At present, the circuit for pre-amplificating the signal picked up by the slider 6 is arranged on the board, or at most on the end of the support body 3, while the microactuator controlling circuitry is integrated with the microactuator. This integration is made possible by silicon microprocessing techniques, such as epitaxial microprocessing or metal electroplating.
The above-mentioned technologies make it difficult, if not impossible, to obtain a group comprising the microactuator-controlling circuitry, the microactuator, the slider, and the pre-amplifying circuit on a same wafer.
In case of epitaxial microprocessing, there is a dimensional incompatibility between the microactuator and the pre-amplification circuit. This incompatibility is due to the fact that the minimum photolithographic dimension of the microactuator is of the order of 1 xcexcm; instead, because of the high operating frequencies, the pre-amplification circuit requires an extreme photolithographic process not exceeding 0.35 xcexcm. The difference between the minimum photolithographic dimensions thus renders integration of the two devices on the same technological platform not very convenient
The metal electroplating technique makes it possible to obtain mechanical structures on the circuitry, but presents certain drawbacks. In fact, it is not possible to effectively protect the micromechanical structures from contamination caused by particles present in the hard-disk driver; assembly of the slider on the microactuator proves difficult; in addition, electrical isolation of the signals supplied by the head from the signals controlling the microactuator is difficult.
An embodiment of the present invention is a process for assembling a micromechanical structure, in particular a microactuator, on a supporting element, in particular an integrated device containing the circuitry, that protects the micromechanical structure at least during assembly.